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Peripheral Architecture
2.4.3Activation (ACTV)
The DDR2 memory controller automatically issues the activate (ACTV) command before a read or write to a closed row of memory. The ACTV command opens a row of memory, allowing future accesses (reads or writes) with minimum latency. The value of DDR_BA[2:0] selects the bank and the value of A[12:0] selects the row. When the DDR2 memory controller issues an ACTV command, a delay of tRCD is incurred before a read or write command is issued. Figure 7 shows an example of an ACTV command. Reads or writes to the currently active row and bank of memory can achieve much higher throughput than reads or writes to random areas because every time a new row is accessed, the ACTV command must be issued and a delay of tRCD incurred.
Figure 7. ACTV Command
ACTV
DDR_CLK |
|
DDR_CLK |
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DDR_CKE |
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DDR_CS |
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DDR_RAS |
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DDR_CAS |
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DDR_WE |
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DDR_A[12:0] | ROW |
DDR_BA[2:0]
BANK
DDR_DQM[3:0]
16 | DDR2 Memory Controller |
